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Brewer, W.M., 1982

Stratigraphy, structure, and metamorphism of the Mount Deborah area, central Alaska Range, Alaska

Bibliographic Reference

Brewer, W.M., 1982, Stratigraphy, structure, and metamorphism of the Mount Deborah area, central Alaska Range, Alaska: University of Wisconsin, Madison, Ph.D. dissertation, 2 vol. (399 p)., illust. (some color), maps, 6 folded maps in pocket.


Rocks of the Mount Deborah area can be separated into four tectonostratigraphic terranes, here called the northern, central, and southern terranes, and the Maclaren belt. These terranes were juxtaposed by movements along thrust and strike-slip faults during late Mesozoic and Cenozoic time. Pre-Upper Cretaceous rocks of the northern terrane are divided into a basal sequence and two overlying thrust nappes. The basal sequence contains silicic metavolcanic and quartzose metasedimentary rocks. The lower nappe contains chert, slate, phyllite, pillowed greenstone, and limestone. The upper nappe contains quartzite, limestone, and phyllite. Jurassic to Cretaceous gabbro intrudes the northern terrane. The central terrane contains Silurian to Devonian quartzite, phyllite, limestone, and strained conglomerate. The southern terrane and Maclaren belt contain diverse metamorphic rocks. Tertiary granitic plutons intrude all terranes. Early Cretaceous(?) northwestward-directed nappe emplacement and moderately high pressure, low-grade metamorphism accompanied juxtaposition of the northern terrane and the previously deformed and metamorphosed central terrane. The southern terrane and Maclaren belt underwent deformation and low pressure, medium- to high-grade metamorphism by Early Cretaceous time. ~300 km of subsequent strike-slip movement along the Hines Creek fault prior to 95 m.y. placed the southern terrane and Maclaren belt close to the northern and central terranes. En echelon folds and reverse faults in the northern and central terranes were produced by <100 km of dextral movement since 95 m.y. ago along an ancestral McKinley fault that now separates the central and southern terranes. Emplacement of a 27 m.y. tonalite pluton aong this ancestral fault was followed by 9 km of dextral displacement on the eastern Hines Creek fault and the Wood River fault. The southern terrane was separated from the Maclaren belt by formation of the present McKinley fault sometime after intrusion of the tonalite pluton. Structures associated with the present McKinley fault include a zone of cataclastic rocks, several reverse faults, and a macroscopic flexure of metamorphic and cataclastic foliations. Dextral displacement on the active McKinley fault totals ~4 km in the Quaternary and ~101 m during the Holocene.

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